My last bug to wig out... speedometer question

[mobileaudio25]

when I bought my car the speedometer wasn't ever hooked up (no cable). So I put one in and didn't ever get it clipped to the back correctly. No I have everything apart and am fixing everything to get this car perfect.

I installed the cable to the back of the speedo correctly and when I put it in gear with the car jacked up and give it gas it goes all the way to the other side of the gauge (85mph+).
If I then put it in reverse it will go back to 0 a little past it.

I have a turbo 350, 373 gears and I'm sure the gears in the transmission are incorrect with my new setup. I bought the transmission used so I have no clue what the previous owner has in there.

The gauge moves freely both ways. Do you guys think my speedometer is bad or I may have bad/broken or the wrong plastic transmission gears?
I'm pretty sure this is my last problem to fix! Thanks for all the help wouldn't have been able to do it without you guys

 

[pontiacgp]

I don't like being the bearer of bad news but that will not be your last bug to figure out. Here is how to figure out what speedo gear your need

lhttp://novaresource.org/speedo.htm

 

[Longroof79]

As Steve pointed out, sounds like a classic case of incorrect speedo drive and driven gears.

 

[mobileaudio25]

As Steve pointed out, sounds like a classic case of incorrect speedo drive and driven gears.

Honestly I would rather it be the gears than the speedometer. I like buying new parts and that's something I haven't replaced.

Would incorrect gears make it that different? If I barely touch the gas the needs goes all the way to the other side. I can't even get it to stay in between 0 and 85 much at all. Still think it's the gears?

 

[mobileaudio25]

I just did the math. 3.73x20.2 = 75.34
245/45r17 is 25.7 in tall
75.34/25.7 = 2.93

How do I know if the gear that's in it now is correct? Is there a certain way to tell what correct driven gear is used for a turbo 350 or should I just pull it and see what gear is in there as far as size?

 

[black_aerocoupe]

In theory, you should be able to get a reading under 85mph consistently even with wrong speedo gears. But, you don't know what parts are good. Yet.

The 3.73 geared g-bodies had a 10/30 speedo gear tooth combination. You may as well see what you have before ordering new. There are 4 types of speedo gears that could end up in a TH350.

 

[mobileaudio25]

I'm going to pull the driven gear out in the morning. I'll let you know what I find out

 

[Jeff L]

My friend's 84 Monte SS came from the factory with the wrong speedo gear installed. He had been on the highway driving to work (55 mph at that time) and he was going his usual 61-62 mph but radar clocked him at 67-68. I remember going with him to the dealer and the car on the lift and the mechanics swapping speedo drive gears in and out trying to get the correct reading. His car was bone stock and they could never figure out why it was reading the wrong speed? His car after the repair was still 1-2 mph off. He never replaced the speedometer because he didn't want his dash messed with since the car was new. It was just one of those scratch your head moments deling with a new car.

Hope you get your issue figured out.

 

[mobileaudio25]

I don't like being the bearer of bad news but that will not be your last bug to figure out. Here is how to figure out what speedo gear your need

lhttp://novaresource.org/speedo.htm

I pulled my speedometer cable and gear housing out. Once apart I hooked the cable to the housing and plastic gear and spun the gear by hand and it felt like there was some push back and I got the needle to move. So it feels like the driven gear is fine and looks to be in good shape physically.

My plastic gear measure roughly 3/4 in diameter and had 22 teeth, it was like and off yellow though no the gray color it says it should be in the link.

Does that mean I need to pull the tail shaft to see what condition the other gear is in? when I put my car in drive I could get the needle to slowly accelerate it was very jump and almost always to the right or the left

 

[pontiacgp]

with a flashlight you should be able to see the other gear on the tail shaft with the gear pulled out